Blockchain definition

A blockchain is a shared digital ledger that records transactions in linked blocks, each cryptographically tied to the one before it and copied across many computers. The result is a record that the whole network holds in common and that is very hard to alter after the fact.

Transactions are grouped into a block, validated by the network, and appended to the chain; each block carries a fingerprint of the previous block, so changing an old record would break every block that follows. Because every participant keeps a copy and the network agrees on which version is correct, no single party controls the record.

A traditional centralised database or ledger is the opposite arrangement: one organisation owns the master copy, controls who can read or write to it, and can edit entries directly. A blockchain spreads that authority across the network and makes past entries append-only rather than freely editable.